1. TECHNICAL FIELD
The invention relates to integrated circuit processing. More particularly, the invention relates to the post etch processing of integrated circuits.
2. DESCRIPTION OF THE PRIOR ART
During the fabrication of an integrated circuit on a semiconductor wafer substrate, interconnections must be made among the various structures that comprise the circuit and to pads that allow the lC to be connected to external circuits and devices. The preferred method for forming these interconnections is through the use of a process, referred to as metallization, in which a conductive material, such as aluminum, is applied to the wafer. Such metallization typically uses a patterning technique that involves a photosensitive material (i.e. photoresist). The patterned surface of the wafer is developed to remove photoresist from those areas that are to be etched. The surface of the wafer is then etched to remove the exposed portion of the aluminum and thereby provide the appropriate connections. Thereafter, excess photoresist may be removed from the surface of the wafer.
Metal etch processes as are discussed above typically use a dry plasma etch technique. The dry plasma etch is anisotropic, i.e. it etches in a fashion that exhibits an accelerated etch rate perpendicular to the surface of the wafer. The gases most commonly used for the dry etch are BCl.sub.3 and Cl.sub.2. The use of radio frequency energy (RF) or microwave energy to excite the etch gas and thereby ignite a plasma that is used for the anisotropic dry etch process is well known in the prior art.
FIG. 1 is a cross section of a wafer 1 after metal etching. During different stages of the lC fabrication process, residues are generated by the material that is being etched, as well as by various chemical components of the etch gasses. These residues can include such materials as silicon byproducts, copper, chlorine, aluminum, and fluorine containing compounds. Additionally, the photoresist that is used to pattern the wafer surface remains on the wafer surface after the metal etch process is completed. Due to the small size and high density of the interconnections, photoresist and small amounts of contaminants remaining on the lC after the metal etch process can interfere with contact formation. It is therefore of critical importance to remove from the surface of the wafer all extraneous processing by-products, such as photoresist and polymers 4, 5 that are built-up on the sidewalls 2 and top surface 3 of the wafer. Unfortunately, these materials are extremely difficult to remove entirely without running the risk of damaging the delicate structures of the lC.
The metallic material that is etched primarily constitutes aluminum, but may also contain a percentage of silicon and copper. These silicon and copper impurities create troublesome compounds in the residues, thereby exacerbating the problem of their removal. Furthermore, because the photoresist is an organic polymer, it also contributes polymer-forming carbon-containing species to the residue.
The current methods of removing photoresist and residue typically involve the use of a downstream oxygen plasma that etches the residue from the surface of the wafer. It is thought that the atomic oxygen produced in the plasma is the primary active species for removing the polymer residue. Thereafter, it is usually desirable to passivate the wafer and thereby inhibit corrosion mechanisms that can damage the wafer.
It would be a significant advance in the art to provide an improved process for simultaneously removing photoresist and polymer residue from the top surface and sidewalls of a post-metal etch wafer. It would be a further advance in the art if such a process removed the photoresist and polymer residue while minimizing such problems as corrosion.